1. Technical Field
The present invention relates to a motion detection apparatus which detects motion at the time of separating a luminance signal and a chrominance signal from a video signal.
2. Related Art
For a color television signal of NTSC and PAL systems, a composite video signal in which a luminance signal and a chrominance signal are multiplexed is used. In order to apply Y/C separation processing, noise reduction processing, and so on, to the composite video signal, motion detection is performed. In a processing called motion-adaptive three-dimensional luminance/chrominance (Y/C) separation, when separating a luminance signal and a chrominance signal, two-dimensional Y/C separation utilizing correlation between horizontal lines and three-dimensional Y/C separation utilizing correlation between frames are switched from one to the other in accordance with a result of motion detection.
For example, motion detection processing, in which an edge is detected and the sensitivity of motion detection is decreased in a region which is determined to be an edge portion, thereby reducing erroneous detection of motion, is disclosed. In another technology, the precision in edge detection is increased by detecting an edge from each of an input signal and an output signal of a frame memory.
Here, a primary factor of erroneous detection of motion at an edge portion when detecting motion from a video signal is crosstalk of a luminance signal and a chrominance signal. For example, in the NTSC system, the phase of a luminance signal is identical between frames, whereas the phase of a chrominance signal is reversed in consecutive frames. As the phase of a chrominance signal is reversed between frames, an inter-frame differential signal includes a motion component and a color component. When a motion detection circuit determines this color component as motion, deficiencies including dot disturbance, cross color, image blur, and so on occur.
In the related art, the level of a motion signal supplied from a motion detection circuit is diminished in accordance with the level of an edge detection signal. The edge detection circuit extracts a change in frequency components associated with a change in a luminance signal and a chrominance signal by a band-pass filter, to thereby extract an edge component.
One problem of the related art is that it is difficult to detect an edge. First, while the signal level of a luminance signal is 100IRE at white peak, the maximum amplitude of a cyan bar and a red bar of a modulation chrominance signal is 63IRE. There is also a problem of a band-pass filter for edge detection. With regard to a design pattern of an image in which a chrominance signal changes in the horizontal direction, the frequency components of a modulation chrominance signal extend to low frequencies. With regard to a design pattern of an image in which a chrominance signal changes abruptly in the horizontal direction, there are cases where an edge cannot be detected unless the band of edge detection is expanded to low frequencies. Conversely, if the band of edge detection is extended to low frequencies to thereby increase the frequencies of edge detection, there is motion in an image and therefore edges of different design patterns in a current frame signal and a previous frame signal may overlap with each other. In this case, in spite of the fact that an image is moving, the presence of an edge is determined and the sensitivity of motion detection is decreased, causing a possibility that the image will not be determined as a moving image.